Energetics

• Metabolic scaling relationships• Behavioral thermoregulation• Torpor and hibernation• Fat storage• Migration• Biological clocks

Discussion Readings

• Kortner, G. and F. Geiser 2000 The temporal organization of daily torpor and hibernation: circadian and circannual rhythms. Chronobiology International 17:103-128.

• Geiser, F. and R.M. Brigham 2000 Torpor, thermal biology and energetics in Australian long-eared bats (Nyctophilus) J. Comp. Phyiol. B 170:153-162.

• Park, K. J., G. Jones, and R. D. Ransome. 2000. Torpor, arousal and activity of hibernating Greater Horseshoe Bats (Rhinolophus ferrumequinum). Functional Ecology 14:580-588.

Aerobic respiration

• Occurs in mitochondria of all aerobic organisms• Glucose + oxygen + water =>

carbon dioxide + water + energy

• C6H12O6 + 6O2 + 6H2O => 6CO2 + 12H2O + energy

• Energy is stored by converting ADP -> ATP• 1 mole of glucose contains 670 kcal• Consequently, oxygen consumption can be used to

measure energy production

Energetics of homeothermy

Energy expenditure in the western pipistrelle (Pipistrellus hesperus)

Homeothermy: maintain constantwarm body temperature. Mostmammals are at 35-39oC

Heterothermic: allow body tempto fall with ambient temperature

Animals must spend energy tokeep warm or cool off when theambient temperature is out of their thermal neutral zone

Thermal conductance

Log-log plot

Heat conduction occurs whenthere is a temperature differencebetween body and air.

Depends on surface area of animal.

Measured as the amount of energyneeded to maintain that difference.

Note that small mammals havehigh conductance due to highsurface area to volume ratios.

Bats have higher conductance thanother mammals due to large lungsand large wing membranes

Metabolic rate scales with body mass.75

Note: if y = aMb thenlog y = log a + b*logM

If b < 1, then y increases slower than M

If b > 1, then y increases faster than M

Therefore, mass specific metabolic rate declines with body size in birds and mammals

Nonflying eutherian mammals

Diet influences metabolic rate

Reasons for energy budget fluctuations

Availability - e.g. seasonality

Demand - e.g. pregnancy

Both - e.g. winter, night

Lactation is costly

Roost selection

Behavioral thermoregulationNycticeius humeralis

Evening bats

Phyllostomus hastatusGreater spear-nosed bats

Torpor is a reduction in body temperature

Torpor saves energy

Energy use increases linearly as ambient temperature decreases for an active animal that maintains a constant body temperature

Arousal from torpor can be expensive

Hibernation = long torpor

Ground squirrel maintained at 4oC

Hibernation has evolved twice in bats

and has allowed some

species to occupy cold

climates

Vespertilionidae

Rhinolophidae

Hibernacula temperature preferences

During hibernation bats maintain body temperature about 1oC above ambient, but rarely below 6oC

Some bats move north to hibernateGray bat (Myotis sodalis)

Bats rarely roost deep in cavesbecause the temperature is toowarm. Consequently, they have to move when it gets cold or warm outside. This makes them vulnerable to disturbance during hibernation.

Body weight during hibernation

Bats can arouse faster than other hibernators

a =ventral temperature, b = rectal temperature

Due to nonshivering thermogenesis

Brown adipose tissue (BAT)contains fat cells with many blood vessels and mitochondria which gives the tissue a brown color.

When BAT is oxidized, the bloodis heated quickly.

Myotis myotis

BAT seasonal accumulation

Myotis californicus

Migration permits other

species to occupy

temperate regions

Molossidae

Phyllostomatidae

Temperate migration patterns

Nyctalus noctulaNoctule

Lasiurus cinereusHoary bat

Migration routes of lesser long-nosed bats (Leptonycteris curasoae)

Feed on cactus going north, agave going south

Biological clocks

• Clock periods– Circannual– Circalunidian– Circadian

• Clock Entrainment

Hibernation follows annual rhythm ingolden-mantled ground squirrels

Five animals were isolated at birth and kept in darkness at 3oC

Circannual clocks in bats

Testes growth and feather molt in

stonechats follows annual cycles

Nestlings were removed from Kenya and reared in Germany with constant temperature and photoperiod and yet retain annual molt and testes cycles.Notice that the clock period drifted.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Kangaroo rat feeding shows lunar cycles

K-rat activity at a feeder is confined to dark periods

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occurred during periodof seed shortages

Vampire bats also avoid moonlight

Entrainment by environmental cycles

• Environmental cues set cycle period– Species specific

• Types of cues– Photoperiod– Light pulse– Food availability

Mouse activity entrains to light

10 mins of light per day are sufficient to reset the clock

12h light:12h dark

24 h dark

10 min light

Frequency of flights within a cave by

Myotis

Note that bats show strongcircadian rhythm before andafter winter

Distribution of circadian clocks in

tissues and taxa

Mammalian clock

pathways

Clock summary

• per/tim/tau(dbt) genes control pacemaker• Pacemaker occurs in SCN (suprachiasmatic nucleus) in

vertebrates, but is distributed in brain cells in some insects

• SCN signals pineal gland to release melatonin• Short pulses of light entrain SCN and pineal cells• Drosophila, honey bees, hamsters and humans share same

genes - likely common ancestor was a flatworm that lived about 600 MYA